The invention is based on a method and on a hydraulic brake booster for feedback of disruptions to the brake pedal characteristic, and hydraulic brake booster.
Brake boosters in general are known from U.S. Pat. Nos. 4,143,514 and 4,482,192. In these known brake boosters, typically one brake circuit is closed and the other is open. The open brake circuit is supplied directly by a reservoir pressure supplied via a control valve or a brake valve. If the pressure supply should fail, the open brake circuit becomes a closed brake circuit. Generally, the open brake circuit includes an annular piston, which is mounted upon a pedal tappet actuated by the brake pedal.
Two basic types of brake boosters can be distinguished: those equipped with a travel simulating spring and those without such a spring, which exerts a perceptible force feedback upon the brake pedal. A problem in brake boosters equipped with travel simulators, which in principle is superior to brake boosters lacking travel simulators, is the lack of feedback of an initially arbitrary disruption in the brake circuit to the brake pedal. That is, disruptions such as the failure of a circuit, poor bleeding because of vapor bubbles, perhaps seizing of the control piston acted upon by brake pressure, and the like, are not perceived by the driver, or at least not at the point at which he himself directly influences braking of his vehicle; in other words, there is no feedback of the pedal characteristic to the driver's braking foot.
Although with such brake boosters having travel simulators it is possible to ascertain failures by evaluating the piston movements in comparison with the movement of the pedal tappet and then to indicate the movement by optical or acoustical signals, still the driver does not necessarily pay attention to such acoustical signals when they occur; also, he tends simply to keep driving, without eliminating the disruption, unless he quite characteristically feels the disruption when actuating the brakes.